How can I prepare clay prone soil to grow red raspberry bushes?

https://www.starkbros.com/growing-guide/how-to-grow/berry-plants/raspberry-plants/soil-preparation

Put in a raised bed.

print PDF of the Raspberry Steps to Success - Nourse Farms

You need to add something to break it up and keep it from going back to solid clay. Use a rototiller. If you don't have one you can rent them from Home Depot. Break up the clay as far down as you can. Even if you get the top amended, the clay will still be under where you have tilled and cause drainage problems. It will take some work! Then add peat moss and sand. The peat moss will help add nutrients and hold water. the sand will help keep the clay loose. Use the tiller to work it into the clay. I can't tell you how much of each, ( more moss than sand) but as you work it in you should be able to see when it's getting to a good soil consistency. Plants like raspberrys are pretty hardy as I remember, so once they are established they should be easy to maintain.

https://www.starkbros.com/growing-guide/how-to-grow/berry-plants/raspberry-plants/soil-preparation

Do not add sand to clay soil, it will bind to the clay particles and create even more problems. I have heavy clay and by adding compost every year it becomes easier to work with. My raspberries, a huge patch I have had for over 20 years do just fine in the clay. The only problem I have is iron deficiency so I add iron in early spring. One thing you should do is contact your local extension service and inquire about a soil test. They will make recommendations specifically for your soil as to adding nutrients and compost. Clay is typically a nutrient rich soil but because of the compacting it's hard for plants to uptake those nutrients. That's where adding compost comes in.

Add compost and work it in, I used coffee grounds, they like slightly higher acid, soil, well draining, with high organic content. Keep the topsoil loose.

A raised bed is easiest. I have clay soil (Oregon) and the best thing to do is a raised bed.